The state of the art methods for preparing mixed metal oxide include use of process by precipitation. Metal sulphate is a cheap pure raw material and good catalysts can be obtained by coprecipitation, but with a too high sulphur level. On the other hand, metal nitrate is an expensive raw material, and dissolving metals in nitric acid require the expensive nitric acid.
The known methods for preparing mixed metal oxide catalysts are costly in terms of purchasing the acid and basic raw materials and after the precipitation, washings and waste-water treatment.
This is described in U.S. Pat. No. 4,482,645, where Jennings et al. prepare a solution of iron nitrate and chromium nitrate, to which sodium carbonate is added and the formed iron and chromium hydroxides are washed before drying and decomposition to oxides.
The general object of this invention is, thus, to provide an improved process for the production of mixed metal oxide containing catalysts by simplified and inexpensive steps. Now an alternative manufacturing route based on metals via nitrates and nitric acid recovery has been invented and developed.
Compared to the known methods, the advantages of the invention include a high quality catalyst, and furthermore, high product yield through reduced loss of material during the processing.